1. Technical Field of the Invention
The present invention relates generally to a structure of a stator for use in a electric rotary machine such as a motor-generator and a electric rotary machine equipped with such a stator for use in, for example, automobiles.
2. Background Art
In recent years, electric rotary machines which are for example used as motor-generators are desired to be miniaturized, produce high-power, and improved in quality.
For example, electric rotary machines for automobiles are required to improve electric power output while space for the electric rotary machine equipped in the engine compartment of the automobile is getting smaller.
Specifically, the miniaturization and production of high-power from the electric rotary machines requires a decrease in winding resistance in each of phase windings of a coil, improvement of the space factor of the phase windings which are disposed within a magnetic circuit of a stator, and close alignment of turned portions of each of the phase windings.
In order to meet the above requirements, electric rotary machines are being studied which have installed therein a stator equipped with a stator core in which a plurality of slots are arrayed in a circumferential direction thereof and a stator coil which is fabricated by a plurality of conducting wires and wound through the slots of the stator core. Each of the conducting wires is made up of in-slot portions to be disposed one in each of the slots and turned portions each of which connects adjacent two of the in-slot portions.
Each of the turned portions of the conducting wire is being developed to include a plurality of steps extending substantially parallel to the surface of either of the ends of the stator core in order to densely-arrange the turned portions to minimize the height thereof above the ends of the stator core.
Adjacent two of the steps of each of the turned portions are connected through an S-curved portion. The S-curved portion has an incurve section which is curved toward the end of the stator core and an outcurve section which is curved away from the end of the stator core. The incurved section is smaller in radius than the outcurve section. Two of the turned portions are arrayed with the incurve and outcurve sections being laid adjacent to each other in a height-wise direction of the stator core through an air gap. The cooling of the stator may be achieved by spraying coolant such as ATF (i.e., automatic transmission fluid) to the stator coil. This causes the coolant to pass also through the air gap between the incurve and outcurve sections. This cooling, however, is not enough to cool the whole of the stator coil. It is also not considered to increase a cooling area of the stator coil.
The steps of each of the turned portions of the conducting wire are usually formed by a press. The pressing will cause the incurve section to have bulges extending perpendicular to a direction in which the curved section extends. The many bulges will be arrayed in a radius direction of the stator core, thus resulting in an increase in size of the stator coil in the radius direction, which disturbs the downsizing of the stator.